Hydrogen-producing fuel processing systems, or assemblies, include a series of devices or components that produce hydrogen gas as a primary reaction product from one or more reactants, or feedstocks. The fuel processing system includes a fuel processing assembly with a hydrogen-producing region that is adapted to convert the one or more feedstocks into a product stream containing hydrogen gas as a majority component. In operation, the hydrogen-producing region is typically operated at an elevated temperature and pressure and contains a suitable catalyst to produce at least hydrogen gas from the feedstock(s) delivered thereto. The produced hydrogen gas may be used in a variety of applications. One such application is energy production, such as by electrochemical fuel cells. An electrochemical fuel cell is a device that converts a fuel and an oxidant to electricity, a reaction product, and heat. For example, fuel cells may convert hydrogen and oxygen gases into water and electricity. In such fuel cells, the hydrogen gas is the fuel, the oxygen gas is the oxidant, and the water is the reaction product. Fuel cells are typically coupled together to form a fuel cell stack.
Hydrogen-producing fuel processing assemblies and systems typically include a series of interconnected functional components that collectively produce hydrogen gas from one or more reactants, or feedstocks. These components include at least one reactor, hydrogen-producing region, or reforming region, in which hydrogen gas is produced by chemical reaction of the feedstock(s), which may be delivered to the hydrogen-producing region in one or more feed streams by a pump or other suitable feedstock delivery system. When a feedstock is a liquid feedstock at ambient conditions, the functional components may include a vaporizer, or vaporization region. A heating assembly, such as a burner, may consume a fuel to produce a combustion exhaust stream that may be used to heat at least the vaporization region, such as at least to a suitable temperature to vaporize the liquid feedstock. When the hydrogen-producing region utilizes an endothermic reaction, such as a steam reforming reaction, it may be thought of as a reforming region and the combustion exhaust stream may be utilized to heat the reforming region to at least a minimum hydrogen-producing temperature. The reformate stream produced by the reforming region may be delivered to a fuel cell stack, and optionally may first be delivered to a separation assembly to increase the hydrogen purity of the stream that is delivered to the fuel cell stack.
Typically, the components of the fuel processing assembly and/or fuel processing system are discrete components that include individual shells or housings and which are interconnected by tubing or similar fluid conduits, fittings, and the like. The entire fuel processing system may be enclosed in a system enclosure or system housing, but the individual components typically are positioned in a spaced-apart relationship within the housing, with the housing defining an open chamber, or cavity, within which the individual components are positioned. The separate structures of these components, and the fluid conduits used to seal and interconnect these components, contribute to the number of parts, potential leak points, assembly time, and manufacturing expense of the fuel processing system. Also, the spatially separated orientation of conventional fuel processing assemblies increases the thermal management needs of the fuel processing system. These needs may be exacerbated by the conventional use of steel alloy housings for components of at least the fuel processing assembly, such as at least the vaporization region and reforming or other hydrogen-producing region thereof. Due to the low thermal conductivity of steel alloys, the surface area of the housing often has to be largely enhanced (e.g., through finned tubes or plate heat exchangers) or a high heat transfer rate has to be imposed on these components (e.g., through direct flame impingement), which may result in increased design cost or lower reliability, respectively.